1. Field of the Invention
Apparatuses consistent with the present invention relate to a low noise amplifier for ultra wide band. More particularly, the present invention relates to a low noise amplifier (LNA) for ultra wide band (UWB), which amplifies signals in the ultra wide band by coupling narrow band LNAs and thus obtains high gain and low noise figure (NF) which are characteristics of the narrow band LNA.
2. Description of the Related Art
With the wide use of Internet and the rapid increase of multimedia data, there is a great demand for very high speed communication networks. Among those networks, a local area network (LAN) has been introduced in the late 1980's. The transfer rate of the LAN was about 1-4 Mbps at the initial phase and has increased to 100 Mbps. As there is an increasing demand for global access to networks due to the prevalence of portable computers and personal digital assistants (PDAs), the wireless communication technology is of great concern.
To respond to those demands, an ultra wide band communication technique which enables wireless communications in high speed wide band together with existing wireless communication services is under development. To distinguish the UWB from the existing narrow band systems and the wide band systems with 3G cellular technology, the UWB is defined as a wireless transmission technology with bandwidth that occupies more than 25% or 1.5 GHz of center frequencies. Primarily, the UWB occupies the frequency band ranging from 3.1 to 10.6 GHz and covers a transmission range of 10 meters through 100 meters.
A wireless terminal used for such wireless communications, as shown in FIG. 1, includes a receiving block 10, a transmitting block 20, a controller 30, a modem 40, and a local oscillator (LO) 50.
The receiving block 10 includes a low noise amplifier (LNA) 11, a mixer 13, and a filter 15. A radio frequency (RF) signal, which is a high frequency signal received via an antenna, has a very low power level due to attenuation and noise. The LNA 11 removes the noise from the RF signal and amplifies the RF signal. The mixer 13 converts the amplified RF signal to an intermediate frequency (IF) signal. The filter 15 filters a required region from the IF signal and provides the filtered region to the modem 40.
The modem 40 converts the IF signal input from the filter 15 to a Rx baseband signal. The modem 40 also converts a Tx baseband signal to be provided to the filter 25 of the transmitting block 20 to an IF signal. The LO 50 receives a control signal and generates LO signals to be fed to the modem 40 and the filter 25.
The transmitting block 20 includes a filter 25, a mixer 23, and a power amplifier 21. The filter 25 filters a required region from the IF signal to be transmitted. The mixer 23 converts the IF signal to the RF signal. The power amplifier 21 amplifies the output so that the RF signal can be transmitted.
The sensitivity of the wireless terminal directly depends on a noise figure (NF), and substantially, noise of the receiving end is determined by the LNA 11. Thus, it is crucial to design the LNA 11 with suitable linearity and gain while the noise is minimized. The related art can design the LNA 11 to meet such requirements in the narrow band mostly used.
With the active development and research on UWB, various LNA designs have been made to implement the LNA available in the UWB.
U.S. Pat. No. 6,735,421 (hereafter, referred to as a prior art 1) titled, “Receiver Including Low Noise Amplifier And Frequency Down-Converter For A Wireless Telecommunication System,” describes a narrow band LNA including a field effect transistor (FET), a resistor R3 and a capacitor C1 for the negative feedback connected in parallel between a gate terminal and a drain terminal of the FET as shown in FIG. 2. The resistor R3 and the capacitor C1 reduce the gain in the low frequency and prevent the amplifier from getting high gain in the low frequency. In other words, the RC feedback design increases the output with respect to the input of the LNA and expands the bandwidth rather than reducing the gain. As a result, the prior art 1 can realize the LNA for the wide band but produces high NF and low gain.
U.S. Pat. No. 6,806,777 hereafter, referred to as a prior art 2 titled “Ultra Wide Band Low Noise Amplifier And Method” discloses a wide band LNA using a common-gate input as shown in FIG. 3. The LNA of the prior art 2 includes a cascode 102 with a load tracking (LT) network 104, and a common-gate part 106. The common-gate part 106 is in a common-gate amplifier arrangement since an RF signal is input to its source and its gate is AC grounded. Hence, the wide band amplifier can be designed since an RFin terminal can match the wide band impedance. However, the LNA of the prior art 2 cannot obtain high gain due to the impedance but produces high NF as the RF signal is input to the source.
Therefore, what is needed is a LNA for the UWB with the high gain and low noise advantages of the narrow band LNA.